We affiliate ourselves with things in our daily lives. Whether it is our place of employment, the school we attend, or the religion we associate with, these affiliations define us and tell something about who we are. These affiliations can also classify us as belonging to a particular group. For example, one would classify an individual that has a Juris Doctor and that works for a law firm as most likely being a lawyer.
These classifications can be useful to tell us something about someone without having any knowledge of the person. It would also be helpful to classify a software program in a similar manner in order to determine which parts of the program are affiliated with a particular software system (without having any prior knowledge of the code).